I've experienced a few seriously strange issues with modern SSDs, even some of the better ones.

I had a 512GB Samsung drive that became very slow randomly at doing IO operations, the whole machine would die for 10-30 seconds at a time once or twice a day while any process that tried to use the disk became blocked on IO. Then it'd come right back like everything was perfectly fine.

Issues like this definitely worry me, we're basically completely blind as to what those controllers and flash chips are actually doing. Not that it wasn't a similar situation with HDD controllers before, but at least it didn't seem as unpredictable.